How long until the ball hits the ground?

  • Thread starter hyde2042
  • Start date
  • #1
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Homework Statement



A ball is thrown downward from a height of 30m at 8m/s. How long until it hits the ground?
(Air resistance is negligible and gravity is 9.8m/s


Homework Equations


I tried deltaX=Vi+(1/2)a(t^2) and came out with 2.12, but the solution says it's 1.79.


The Attempt at a Solution



30=8+(1/2)(9.8)(t^2)
22=4.9(t^2)
sqrt4.49=sqrt(t^2)
t=2.12
 

Answers and Replies

  • #2
CompuChip
Science Advisor
Homework Helper
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Are you not missing a t?
[tex]V = V_i + a t[/tex]
so
[tex]\Delta x = V_i \mathbb{t} + \frac12 a t^2[/tex]
 
  • #3
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Thank you, but I'm afraid I'm evenb more confused by the additional t.

I ended up at 30-8t=4.9(t^2)

What I keep doing after that seems to make it more complicated than it should be. COuld you possibly point me in the right direction? Thank you for your time.
 
  • #4
CompuChip
Science Advisor
Homework Helper
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It's a standard quadratic equation, of the form ax2 + bx + c = 0.
How do you solve one of those?
 
  • #5
26
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Ah... hate when I over look simple things. Thank you very much.
 

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